Ignition resistant carbonate polymer compositions are known, for example see U.S. Pat. Nos. 5,061,745; 6,596,794; 6,727,301; 6,753,366; and Re 36,188. These patents describe compositions comprising a carbonate polymer, a graft polymer, a phosphorus compound, and Teflon. For many years, ignition resistant carbonate polymer compositions have enjoyed widespread success in applications such as electronic equipment, appliance, and tool enclosures and components. In addition to providing an attractive housing for such articles, these enclosures may also play important structural roles. Additionally, one of the key requirements these enclosures must fulfill is, in the event that the electronics in an electronic article fail and catch on fire, the ignition resistant carbonate polymer enclosure must contain the fire so that it does not spread outside of the electronic article. If an electronic article enclosure catches fire and begins to drip and the drip is a flaming drip, the fire can easily spread and endanger both life and property.
These types of ignition resistant carbonate polymer compositions typically need to meet flammability requirements from one or more regulatory agency, for example Underwriter's Laboratories. The procedure in Underwriter's Laboratories Standard 94 (UL 94) characterizes a materials ease of ignition, and once ignited, its burning characteristics, i.e., is the material self extinguishing, how long does it burn, does it drip and if it drips, are they flaming drips.
Phosphorus compounds successfully minimize the ease of flammability in ignition resistant carbonate compositions by gas phase (as a free radical scavenger) and/or solid phase (promoting crosslinking) mechanisms. However, carbonate compositions, being thermoplastic, are predisposed to dripping when heated. Teflon, preferably a fibril forming type, has been very successfully used as an anti drip agent. Generally, with few exceptions, Teflon is found in all of the prior art describing ignition resistant carbonate polymer compositions.
However, as effective as Teflon is as an anti drip agent, it has several drawbacks related to both ease of handling during manufacturing of the ignition resistant carbonate composition (e.g., fouling airvey systems and during extrusion, bridging in the feed hopper throat) as well as several detrimental effects to the physical and aesthetic properties of the ignition resistant carbonate composition, especially in a fabricated article (e.g., reduced impact properties and pitting on the surface of fabricated articles). To compensate for reduced impact properties, often times it is necessary to include an impact modifier to the ignition resistant carbonate polymer composition which increases the complexity and cost to manufacture such compositions.
US Publication No. 2005/0250908 discloses an attempt to solve premature fibrillation and agglomeration of Teflon used as a processing aid in olefin polymers. However, such olefin polymer compositions can not meet the demanding physical, mechanical, thermal, flammability, and aesthetic requirements for applications such as electronic equipment, appliance, and tool enclosures and components.
An attempt to minimize the detrimental effect of the Teflon in ignition resistant carbonate compositions is disclosed in U.S. Pat. No. 6,828,366 wherein the amount of Teflon is reduced, however an additional inorganic material, e.g., talc, is required and mechanical and flammability properties are inferior. An attempt to eliminate Teflon and replace it with flake-form fillers such as mica and/or glass flakes, optionally also in combination with glass fibers is disclosed in U.S. Pat. No. 5,961,915. However, there is no information as to the quality of the flame resistance of the carbonate polymer compositions, in particular regarding the tendency to drip burning material. Also the high inorganic filler content of the carbonate polymer compositions described affects negatively some mechanical properties, for instance impact strength which for many applications is inadequate. WO 99/57198 describes ignition resistant carbonate polymer compositions comprising a phosphorus compound and a low amount of Teflon. However, such compositions have poor resistance to ESC and inadequate heat resistance, as well as a melt stability which is frequently inadequate, in particular for extrusion applications.
It would be desirable to have an ignition resistant carbonate polymer composition comprising an anti drip agent which is easy to handle during manufacturing but does not diminish the physical, mechanical, thermal, flammability, and aesthetic properties of the ignition resistant carbonate polymer, especially for said composition in the form of a fabricated article.